Wet adhesion promoters for emulsion polymers

ABSTRACT

Monoethylenically unsaturated copolymerizable monomers are disclosed which improve the adhesion of copolymers (especially those produced by aqueous emulsion copolymerization to provide latex paint). These monomers are the reaction product of one equivalent of a monoethylenically unsaturated compound which resists homopolymerization and which carries a single isocyanate-reactive hydrogen atom, such as 2-hydroxypropyl monobutyl maleate, one mole of an organic polyisocyanate, such as 2,4-toluene diisocyanate, and sufficient alkyl alkylene urea carrying a single isocyanate-reactive hydrogen atom on the alkyl group, such as 2-hydroxyethyl ethylene urea, to consume the remaining isocyanate functionality on the polyisocyanate. An improved method of producing these monomers from a mixture of all three reactants is also disclosed.

DESCRIPTION

1. Technical Field

This invention relates to monoethylenically unsaturated copolymerizablemonomers which enhance the adhesion of emulsion copolymer latices to anunderlying substrate, to the production of such monomers, and tocopolymers containing the same.

2. Background Art

The emulsion copolymerization of monoethylenically unsaturated monomersto produce latex emulsions for paints is well known. It is also known toinclude a small proportion of a monoethylenically unsaturatedamine-functional monomer in the monomers which are copolymerized inorder to improve the adhesion (both wet and dry) of the latex paint tothe substrate which is painted. The objective is to provide the greatestimprovement in adhesion in the simplest and most effective manner, thecost being a material factor in achieving this objective.

The prior efforts in this direction are illustrated by U.S. Pat. No.3,356,653 to K. Sekmakas, but there are many other patents which areconcerned, in one way or another, with the same problem.

A recent patent of interest is U.S. Pat. No. 4,319,032 to J. M. Sandriet al. in which the adhesion-promoting monomer is produced by thereaction of an omega aminoalkyl alkylene urea, such as 2-aminoethylethylene urea, with an unsaturated glycidyl ether or ester, such asallyl glycidyl ether. It is desired to avoid the use of glycidylcompounds while achieving superior adhesion in a practical fashion, andto do so while retaining the use of an alkyl alkylene urea compoundwhich provides a convenient and economical starting reactant.

DISCLOSURE OF INVENTION

In accordance with this invention, a monoethylenically unsaturatedcopolymerizable monomer having the capacity to improve the adhesion ofcopolymers containing from 0.1% to 10% thereof, is the reaction productof one equivalent of a monoethylenically unsaturated compound whichresists homopolymerization and which carries a singleisocyanate-reactive hydrogen atom, one mol of an organic polyisocyanate,and sufficient alkyl alkylene urea carrying a single isocyanate-reactivehydrogen atom on the alkyl group to consume the remaining isocyanatefunctionality on the polyisocyanate. It is particularly preferred thatthe isocyanate-reactive hydrogen atom be supplied by the hydroxy group.

While the specific procedure used may vary (the polyisocyanate can bereacted first with either of the other reactants and then with theother, or with both at the same time as detailed hereinafter), thereaction product has the following formula: ##STR1## in which

R₁ is alkylene having 2 or 3 carbon atoms, preferably 2 or 3;

R₂ is alkylene having 2 to 10 carbon atoms;

X is a radical which initially carried Z, such as ##STR2##

Z is an isocyanate-reactive hydrogen atom initially carried by R₂ X;

a is an integer from 1 to 5, such as 1 or 2, to consume all theisocyanate groups on the polyisocyanate noted hereinafter other than theone consumed by R₃ ;

Q is an organic aliphatic or aromatic polyisocyanate carrying a+1isocyanate groups;

V is an isocyanate-reactive hydrogen atom initially carried by R₃ ; and

R₃ is the residue of a monohydroxy C₁ -C₁₂ alkyl maleate or fumaratewhich is connected to Q via its hydroxy group; and X and R₃ areconnected to Q via the isocyanate groups therein and Z and V are carriedby the nitrogen atoms in said isocyanate groups.

In preferred practice, R₃ is a derivative of maleic or fumaric acid,most preferably a derivative of monoalkyl maleate or fumarate.

In accordance with the preferred practice of the invention, the alkylalkylene urea is 2-hydroxyethyl ethylene urea which provides a primaryhydroxyl group, and the monoethylenically unsaturated compound is aderivative of monoalkyl maleate or fumarate, such as hydroxy propylmonobutyl maleate, which provides a secondary hydroxyl group. Allylalcohol and 2-hydroxypropyl ethylene area will further illustratematerials which may be used. The polyisocyanate may be either aliphaticor aromatic, but aliphatic polyisocyanates are preferred. It is alsopreferred to employ tri-isocyanates, because these provide the capacityto combine two alkylene urea groups with a single ethylenicallyunsaturated group.

Referring more particularly to he polyisocyanates which can be used, theseveral isocyanate groups may possess the same order of reactivity, asin 1,6-hexane diisocyanate, and the two other reactants can be reactedwith these isocyanate groups, one at a time. Then, one can purify toobtain the desired monoethylenic derivative. While this is possible, itis better to employ an organic polyisocyanate which contains oneisocyanate group which is more or less reactive than the otherisocyanate groups. These are illustrated by isophorone diisocyanate,2,4-toluene diisocyanate, and the trimer formed by reacting three molesof an aliphatic diisocyanate, such as 1,6-hexane diisocyanate, with onemole of water. 2,4,6-toluene triisocyanate is also useful. Then, one canfirst react one of the two other reactants with the more reactiveisocyanate group and then bring in the second other reactant with theother isocyanate groups which are less reactive. This is a conventionalprocedure which is easily used herein in known manner, but it ispreferred to have all the reactants together and to carry out thereaction in two stages, as will be described, for this is simpler andmore economical.

In this improved process, the organic polyisocyanate including at leastone isocyanate group which is more or less reactive than the others isadded slowly to a mixture of the other two components in which theisocyanate-reactive hydrogen atom of the monoethylenically unsaturatedcompound is more or less reactive than the isocyanate-reactive hydrogenatom of the alkylene urea derivative. The polyisocyanate is preferablyselected to include one isocyanate group which is less reactive than theothers, and the proportion of the alkylene urea derivative isstoichiometrically related to the more reactive isocyanate groups in thepolyisocyanate. On the other hand, if the polyisocyanate includes onemore reactive isocyanate group, as in 2,4,6-toluene triisocyanate, theproportion of the alkylene urea derivative is stoichiometric withrespect to the less reactive isocyanate groups in the polyisocyanate. Inthis way, and especially when one uses a polyisocyanate having one lessreactive isocyanate group with an alkylene urea derivative containing aprimary hydroxy group, such as hydroxyethyl ethylene urea, and a maleateor fumarate derivative containing a secondary hydroxy group, such as2-hydroxypropyl monobutyl maleate, then a pure monoethylenicallyunsaturated product is obtained even though the customary two-stagereaction is not performed.

In practice, sufficient amounts of a solvent, such as methyl ethylketone and/or butanol, is used in the production of the monomers toprovide a fluid liquid mixture. Temperatures up to about 60° C.,preferably from 40° C. to 50° C., can be used to react the more reactiveisocyanate group with a primary hydroxyl group or with one hydrogen atomof a primary amine, but higher temperatures, up to about 80° C., areuseful to react a less reactive isocyanate group with secondary hydroxylor carboxyl. Catalysts for the isocyanate reaction, such as dibutyl tindilaurate, are well known and are normally present to aid the reaction.The choice of catalyst and the selection of the active hydrogen atomwith which reaction will be had will vary the temperature which shouldbe employed somewhat, but this is easily adjusted as known to the art.

The monomers of this invention may be incorporated in small proportion,preferably from 0.5% to 5%, by addition copolymerization into polymerswhich consist essentially of copolymerized monoethylenically unsaturatedmonomers. While the polymerization process may be of diverse types, suchas solvent solution polymerization, it is preferred that the copolymerbe formed by aqueous emulsion copolymerization. In this way thecopolymers are provided in the form of an aqueous latex which isstabilized by the presence of surfactants, as illustrated in the patentsnoted previously. Latex paints which coalesce at room temperature areparticularly desired, and for this purpose the monmers of the copolymerand their proportions are selected to provide the copolymer with a T_(g)(glass transition temperature) in the range of -20° C. to +20° C.,preferably in the range of -10° C. to +10° C.

In typical commercial practice, at least about 90% of said copolymerizedmonomers are selected from C₁ -C₈ alkyl esters of acrylic andmethacrylic acids, such as ethyl acrylate, butyl acrylate and methylmethacrylate, vinyl acetate, and ethylene.

Adhesion is of special importance in interior latex paints of semi-glasscharacter which can be expected to be applied over glossy oil-basedpaints which are difficult to adhere to. The examples will thereforeemphasize copolymers of vinyl acetate and butyl acrylate which arefrequently used in such semi-gloss paints.

Traces of residual isocyanate functionality which may remain at the endof the reaction are removed by reaction with an alcohol, and as butanol,or other solvent-type alcohol.

The invention is illustrated by the examples which follow:

EXAMPLE 1

Charge to a reactor equipped with a reflux condenser 130 grams (1 Equiv.OH) of 2-hydroxyethyl ethylene urea, 230 grams (1 Equiv. OH) of2-hydroxypropyl-mono-n-butyl maleate and 180 grams of methyl ethylketons. Set the reflux condenser and heat the mixture to 50° C. withagitation. Add slowly (over a 45-minute period) 174 grams (2 Equiv. NCO)of 2,4-toluene diisocyanate. Hold for 2 hours at 50° C., then heat to70° C. and hold for one hour. Add 50 grams of butanol and hold 1 hour.Cool to 30° C. and store. A solution product was obtained containing69.8% non-volatile solids.

EXAMPLE 2

Charge to a reactor equipped with a reflux condenser 260 grams (2 Equiv.OH) 2-hydroxyethyl ethylene urea, 230 (1 Equiv. OH)2-hydroxypropyl-mono-n-butyl maleate and 375 grams methyl ethyl ketone.Set the reflux condenser and heat the mixture to 50° C. with agitationusing a nitrogen sparge. Add slowly (over a 1-hour period) 760 grams (3Equiv. NCO) [See Note 1 for a description of the aliphatic triisocyanateused.] Hold for 2 hours at 50° C. Heat to 70° C. and hold for one hour.Add 100 grams butanol and hold for 30 minutes at 70° C. Cool to 30° C. Asolution product was obtained containing 63.5% non-volatile solids.

Note 1

The aliphatic triisocyanate is the reaction product of 3 moles of1,6-hexane diisocyanate with one mole of water, the reaction liberatingcarbon dioxide. One of the three isocyanate groups in this triisocyanateis less reactive than the other two. The Mobay product Desmodur N may beused. In this instance it is used in a 75% solution which would bedesignated N-75. The solvent is an equiv. weight mixture of2-ethoxyethanol acetate and xylol.

EXAMPLE 3

Charge to a reactor equipped with a reflux condenser 130 grams (1 Equiv.OH) 2-hydroxyethyl ethylene urea, 230 grams (1 Equiv. OH)2-hydroxypropyl mono-n-butyl maleate and 180 grams methyl ethyl ketone.Set the reflux condenser and heat the mixture to 50° C. with agitation.Add slowly (over a 45-minute period) 222 grams (2 Equiv. NCO) ofisophorone diisocyanate. Hold for 2 hours at 50° C., then heat to 70° C.and hold for one hour. Add 50 grams butanol and 30 grams methyl ethylketone. Hold for 30 minutes at 70° C., Cool to 30° C. and store. Asolution product was obtained containing 69.0% non-volatile solids.

When the monomers of this invention are added to the monomer mixturewhich is copolymerized in aqueous emulsion (as illustrated in U.S. Pat.No. 3,356,653), the wet adhesion properties of paints made from theresulting latices is greatly improved. This has been evaluated in aseries of latex paints which have been pigmented in standard fashion toprovide a semi-gloss paint. In each instance, the latex was based on anaqueous emulsion copolymer containing from 54% to 55% of non-volatilesolids and having a pH of about 7.0 and which is made from a monomermixture containing 84 parts vinyl acetate, 14 parts n-butyl acrylate and2.0 parts of the monomer providing improved wet adhesion.

The results are tabulated in the tables presented hereinafter in whichadhesion of the cured film to a glossy oil-base paint substrate ismeasured in two fashions, namely: by the Wet Slide and Wet Peel Tests.These tests are standard industry tests in which the coating is cut in aline, immersed in water and then an effort is made to remove as much ofit as possible either by sliding abrasion or by an effort to peel itaway with the fingernails. The test results are reported on a scale of 0to 5, 0 denoting complete removal of the film and 5 indicating that nofilm has been removed. Two controls are used in the tabulation. Thefirst control employs the ester of 2-hydroxy ethyl ethylene urea withmaleic anhydride which is then esterified with 1,2-propylene oxide inaccordance with the teachings of U.S. Pat. No. 3,356,653. The secondcontrol is identified as a commercial emulsion which is presently beingused in commerce for semi-gloss paints of the character underconsideration.

                  TABLE I                                                         ______________________________________                                        WET ADHESION TEST                                                             Emulsion Control   Commercial                                                 Tested   No. 1     Emulsion   Ex. 1 Ex. 2                                                                              Ex. 3                                ______________________________________                                        Wet Slide                                                                              3         0          2     5    3                                    Wet Peel 3         0          2     5    3                                    ______________________________________                                    

The above tests were repeated using a different semi-gloss paintformulation to obtain the following results.

                  TABLE II                                                        ______________________________________                                        WET ADHESION TEST                                                             Emulsion Control   Commercial                                                 Tested   No. 1     Emulsion   Ex. 1 Ex. 2                                                                              Ex. 3                                ______________________________________                                        Wet Slide                                                                              2         1          2     4    2                                    Wet Peel 3         1          3     4    2                                    ______________________________________                                    

As can be seen from the tabulated data, all of the adhesion promotersprovide a significant improvement over the commercial control. It willfurther be seen that the monomers of this invention provide resultswhich are at least approximately as good as those obtainable in theprior art referred to. Results will vary, as shown, depending upon thespecific paint formulation, and this raises the prospect that themonomers of this invention will be advantageous in sme formulations. Thetabulated data also shows an outstanding improvement when atriisocyanate is used to provide a monomer product having two ethyleneurea derivatives joined to a single monoethylenically unsaturated group.

As a matter of interest, Examples 1, 2 and 3 have been repeated usingone equivalent of 2-hydroxy ethyl methacrylate in place of oneequivalent of 2-hydroxypropyl-monobutyl maleate. The reaction mixturegelled in each instance to form an insoluble and useless product. In therepeat of Example 2, gellation occurred before addition of thetriisocyanate was complete. The tendency of the monomer known to formhomopolymers to this while the reaction with isocyanate functionality isin progress in the presence of the amine-functional alkylene urea simplyis to strong to allow useful products to be produced.

What is claimed is:
 1. A monoethylenically unsaturated copolymerizablemonomer having the formula ##STR3## in which R₁ is alkylene having 2 to3 carbon atoms;R₂ is alkylene having 2 to 10 carbon atoms; X is aradical selected from NH--, S--, and O-- which initially carried Z; Z isan isocyanate-reactive hydrogen atom initially carried by R₂ X; a is aninteger from 1 to 5 to consume all the isocyanate groups on thepolyisocyanate noted hereinafter other than the one consumed by R₃ ; Qis an organic aliphatic or aromatic polyisocyanate carrying a+1isocyanate groups; V is an isocyanate-reactive hydrogen atom initiallycarried by R₃ ; R₃ is the residue of a monohydroxy C₁ -C₁₂ alkyl maleateor fumarate which is connected to Q via its hydroxy group; and X and R₃are connected to Q via the isocyanate groups therein and Z and V arecarried by the nitrogen atoms in said isocyanate groups.
 2. A monomer asrecited in claim 1 in which X is
 0. 3. A monomer as recited in claim 1in which R₁ contains 2 carbon atoms.
 4. A monomer as recited in claim 1in which R₂ contains 2 carbon atoms.
 5. A monomer as defined in claim 1in wnhich X is 0 and R₁ and R₂ each contain 2 carbon atoms.
 6. A monomeras recited in claim 1 in which a is
 1. 7. A monomer as recited in claim5 in which a is
 1. 8. A monomer as recited in claim 1 in wnhich R₃ isthe residue of hydroxy propyl mono C₂ -C₄ alkyl maleate.
 9. A copolymerconsisting essentially of copolymerized monoethylenically unsaturatedmonomers including from 0.1% to 10% of the monomer recited in claim 1.10. A copolymer as recited in claim 9 in which said copolymer is formedby aqueous emulsion copolymerization.
 11. A copolymer as recited inclaim 10 in which said copolymer has a T_(g) in the range of -20° C. to+20° C.
 12. A copolymer as recited in claim 11 in which at least about90% of said copolymerized monomers are selected from the groupconsisting of C₁ -C₈ alkyl esters of acrylic and methacrylic acids,vinyl acetate, and ethylene.
 13. A copolymer as recited in claim 12 inwhich said copolymer has a T_(g) in the range of -10° C. to +10° C.